Sputtering target and method of manufacturing the same

ABSTRACT

According to the present invention, metal silicide grains are coupled with each other in a linked manner so as to provide a metal silicide phase, and Si grains forming a Si phase are dispersed in the gaps of the metal silicide phase discontinuously so as to provide a mixed structure of a sputtering target of high density and containing carbon at a rate less than 100 ppm. Because of the high density and high strength of the target, generation of particles at the time of sputtering can be reduced, and because of the reduced content of carbon, mixing of carbon in a thin film formed by the sputtering can be prevented.

TECHNICAL FIELD

The present invention relates to a sputtering target and a method ofmanufacturing the sputtering target. More specifically, to a sputteringtarget of high density and high quality adapted to be used for formingthin films as electrodes and wiring members of semiconductor devices,and a method of manufacturing this type of sputtering target.

BACKGROUND TECHNIQUES

Sputtering method has been heretofore used in forming electrodes orwirings of semiconductor devices. Since the method is advantageous formass-production, and for assuring safety of the film thereby produced,it has been used where argon ions are forced to collide againstrefractory metal silicide type target so as to release the metal, and todeposite the same on a substrate opposing to the target in the form of athin film. Thus, it is apparent that the property of the silicide filmformed by sputtering substantially depends upon the property of thetarget.

However, according to increase in degree of integration and minimizationof the integrated semiconductor elements, reduction of particles (minutegrains) generated from the sputtering target, in a case of forming arefractory metal silicide thin film, is urgently demanded. The reason ofthis resides in that the minute particles of approximately from 0.2 to10 μm generated from the target during the sputtering process tend to bemixed in the deposited thin film, and to cause shortage or disconnectionof wiring when the semiconductor device is practically used in acircuit, thus reducing the production yield of the target.

Conventionally, various methods have been proposed for manufacturingtargets of high density, and the structure of which is made compact andfine, so that the amount of particles generated from the target isreduced.

For instance, Japanese Patent Laid-Open No. 179534/1986 discloses amethod wherein a melted Si is impregnated in a semi-sintered rawmaterial made of a refractory metal component (M) and Si component.According to this method, a structure having spherical or oval shapedMSi₂ of grain diameter 5 to 500 μm dispersed in continuous matrices ofSi is obtained, and the amount of contained impurities such as carbonand oxygen is held less than 50 ppm.

On the other hand, Japanese Patent Laid-Open No. 219580/1988 discloses atechnique wherein a mixture made of a refractory metal (M) and Si issubjected to a silicide reaction under a high vacuum thereby forming asemisintered substance, and this substance is thereafter subjected to ahot isostatic press sintering process for obtaining high density oftarget. In this case, a compact structure with the maximum grain size ofMSi₂ held less than 20 μm and the maximum grain size of free Si heldless than 50 μm is obtained. This target has a mixed structure of minuteMSi₂ grains and free Si grains dispersed with each other, and thecontaining amount of Oxygen set less than 200 ppm. Since the Oxygencontent of the target is thus suppressed to a low level, the sheetresistance of the resultant thin film can be maintained in a low level.

Furthermore, Japanese Patent Laid-Open Nos. 179061/1988 and 39374/1989disclose a technique wherein a powdered mixture of a refractory metal(M) and Si is subjected to a silicide reaction under high vacuum, so asto obtain a sintered substance, and this substance is pulverized andadded with a composition adjusting silicide powder, and then subjectedto a hot-press sintering process so as to obtain a target of highdensity and Si coagulation suppressed.

However, in the case of the method wherein melted Si is impregnated in asemi-sintered substance, it is found that although a high density targetcan be obtained as a result of substantial reduction of impuritycontents such as carbon, oxygen and the like. The silicon (Si)impregnated in the semi-sintered substance tends to drop outcontinuously so as to form a matrix; and also that since coarse andlarge Si portions are formed by Si impregnated in large voids formed inthe semi-sintered substance, the Si having a rigidity comparativelysmaller than the metal silicide tends to be broken down by the thermalstress caused during the sputtering process, and furthermore since theSi is provided continuously, the strength of the entire target is madeinsufficient.

Thus, the metal silicide is easily collapsed, and a great number ofparticles are thereby produced.

In case of the method wherein a semi-sintered substance formed by use ofpulverized Si powder as it is for press-sintering, it is also found thatalthough a target of high density and compact structure can be obtained,contaminating carbon mixed during the pulverizing process of Si is notremoved, but it remains in the target, and therefore during thesputtering operation, sputtering drops are not sputtered sufficientlyfrom a portion containing much carbon, thus causing generation ofparticles, and furthermore there is a problem that the carbon containingportion formed in the thin film is hardly etched, thus resulting etchantremain and dis-connection of wiring.

In addition, it is also found that in the case where the pulverized Sipowder is formed into a semi-sintered substance, and the semi-sinteredsubstance is not pulverized, but as it is subjected to press-sintering,although a target of high density and compact structure can be obtained,carbon adversely mixed during the pulverizing step of Si is not removed,but is remained in the target. As a consequence, there arises furtherproblem that sputtering drops are not sufficiently sputtered at aportion containing large amount of carbon, and furthermore, a portion ofthe thin film containing carbon is hardly etched, thus causing presenceof residual etchant, and disconnection of wiring.

In the case where pulverized Si powder is formed into a semi-sinteredsubstance, thus obtained semi-sintered substance is again pulverized, acomposition adjusting silicide power is added thereto, and the entiretyis subjected to a hot-press sintering process; it is also found thatalthough a target of high density and fine structure can be obtained,not only contamination of the material due to carbon increases, but alsothe content of oxygen mixed into the material increases because of thetwo crashing steps. Accordingly, the generated amount of particlesincreases, and the electric resistance of the thin film increasesbecause of oxygen mixed in the thin film.

Even in the case of high density target having a density ratio of 99%,it is also confirmed that the generated amount of particles tends toincrease under the effect of a specific impurity, and waste products areliable to increase rapidly at a time when a wiring pattern is formed byetching on the thin film.

Heretofore, in view of easiness of control of the composition of thesilicide film, a sputtering target manufactured according to apowder-sintering method has been ordinarily used. More specifically, theconventional metal silicide target has been produced by a method whereina metal silicide (hereinafter noted MSi₂) obtained by reactionsynthesizing metal powder (M) of tungsten, molybdenum and else withsilicon power (Si) is subjected together with Si to hot-press or hotisostatic press (Japanese Patent Laid-Open Nos. 141673/1986,141674/1986, and 178474/1986 and else) or a method wherein Si isimpregnated into a silicide semi-sintered substance (Japanese PatentLaid-Open No. 58866/1986).

However, in the case of the former method, since the sintered substanceis provided by adding Si powder to a synthesized MSi₂ powder, in a caseof sintered substance of, for instance, a Composition containing MSi₂.2-MSi₂.9, the occupied volume ratio of Si phase is held in a range of 8%to 25%, much smaller than that of the MSi₂ phase. Accordingly, in orderto sufficiently distribute the Si phase around MSi₂ grains of angularshape obtained by pulverizing, a procedure depending on the presssintering is not sufficient, and a target having defective andnonuniform structure such as including coagulated portion of angularMSi₂ grains and localized portion of Si phase is thereby obtained.

On the other hand, melting point of the MSi₂ phase is much differentdepending on the kind of the metal M. For instance, the melting pointsof WSi₂, MoSi₂, TiSi₂ and TaSi₂ are 2165° C., 2030° C., 1540° C, and2200° C., respectively. In a case where an MSi₂ having melting pointthus differing in a wide range and the Si phase of a melting point of1414° C. are press-sintered at a temperature lower than the eutectictemperature, sintering does not progress between MSi₂ grains ofthermally stable, thus reducing the combining strength between grainssubstantially, and rendering the products to be brittle. Further theremaining pores render the compactness of the structure to beinsufficient.

When a silicide film is formed by sputtering utilizing the thus obtainedtarget, the combination between grains tends to be broken by irradiatingenergy of argon ions, and particles are generated from the sputteringsurface of the target due to breakage and collapse starting from theaforementioned defective portions.

Particularly in a case of a high density integrated circuit and thelike, the width of electrodes and the spacing between wirings areminimized in accordance with an increase in degree of integration from 4Mega to 16 Mega, and therefore, the particles mixed in the depositedthin film deteriorates the yield of production rapidly.

In the case of the latter-mentioned conventional method, the compositionof the target is controlled by impregnated melted Si in the silicidesemi-sintered substance which has been before hand controlled to apredetermined density. However, in a case where MSi₂ is synthesized bysilicide reaction between the M powder and Si powder for obtaining asemi-sintered substance of a predetermined density, or Where asemi-sintered substance or a predetermined density is formed by thesintering process of press-formed MSi₂, the density is varied dependingon the treating temperature and time and the pressing pressure, so thatit is extremely difficult to obtain a target of a desired composition.

According to the knowledge of the inventor of this invention, since thepowdered MSi₂ and Si to be used as materials are of high purity, thereis no tendency of impurities being collected by diffusion in theboundary between MSi₂ phase and Si phase of the target, and thereforethe interface bonding strengths between the MSi₂ phase and the Si phase,and between different MSi₂ phases are made weak.

In addition, there is problem that the sputtering operation becomesunstable, because the difference in electric resistance between the MSi₂phase and Si phase is extremely large. More specifically, the electricresistances of WSi₂, MoSi₂, TiSi₂, TaSi₂, constituting the MSi₂ are 70,100, 16 and 45 μΩ.cm of comparatively small values, respectively, whilethe electric resistance of the Si phase is extremely large value of3×10¹⁰ μΩ.cm. Further, there is no interface layer between the MSi₂phase and the Si phase, so that the electric resistance in the boundaryportion changes abruptly. Particularly in the structure of the targetmanufactured in accordance with the latter method, it is held in a statethat Si phase of high resistance is directly in contact with the MSi₂phase of low resistance.

Accordingly, when sputtering is carried out by use of such target,insulation break-down between the MSi₂ phase and the Si phase inevitablyoccurs under a voltage larger than a predetermined value, and anelectric current starts to flow abruptly. That is, when the voltagebecomes more than a predetermined value, discharge of electricityoccurs, and MSi₂ grains of weak interface bonding strength or parts madeof Si phase are liable to be collapsed, thus generating the particles.

This invention is made in view of the above described difficulties ofprior art, and the object of the invention is to provide a sputteringtarget of high quality capable of substantially preventing generation ofparticles, and capable of forming a thin layer of high quality. Anotherobject is to provide a method for manufacturing such a sputteringtarget.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided a sputteringtarget characterized in that metal silicide (of a stoichiometriccomposition expressed by MSi₂ where M designates a metal) is coupledtogether in a link form to provide a metal silicide phase Si; phase madeof Si grains is dispersed in the gaps of the silicide phasediscontinuously so as to provide a compact mixed structure of thetarget; and carbon content in the structure is restricted less than 100ppm.

Further, metal silicide grains of a number falling in a range of from400 to 400×10⁴, each having a grain diameter of from 5 to 30 μm, areprovided in a sectional area of 1 mm² of the mixed structure, and themaximum grain diameter of Si is restricted less than 30 μm.

Preferably, the average diameter of the metal silicide grains is held ina range of from 2 to 15 μm, while the average diameter of the Si grainsis held in a range of from 2 to 10 μm.

In the above description, grain diameter is defined to be a diameter ofa smallest circle circumscribing the grain.

Preferably, the density ratio of the target is more than 99%, and oxygencontent is restricted less than 150 ppm.

Further, the metal (M) forming the metal silicide is at least one kindselected from a group of tungsten, molybudenum, titanium, zirconium,hafnium, niobium, tantalm, vanadium, cobalt, chromium and nickel.

Preferably, an interface layer is formed between the metal silicidephase and the Si phase, and the thickness of the interface layer is setin a range of from 100 to 10000Å.

Preferably, the Si phase contains at least one kind of element selectedfrom a group of B, P, Sb and As, and unavoidably contained elements, andthe electric resistivity of the Si phase is restricted in a range offrom 0.01 to 100 Ω.cm.

Further, there is provided a sputtering target manufacturing method ofthis invention, capable of manufacturing a sputtering target, whereinmetal silicide (of a stoichiometric composition expressed by MSi₂, whereM represents a metal) is coupled with each other in a link form toprovide a metal silicide phase, a Si phase made of Si grains is held inthe gaps of the silicide phase discontinuously so as to provide acompact and minute mixed structure of the target, and carbon content inthe structure is restricted less than 100 ppm.

Preferably, the method for manufacturing the sputtering targetcomprises:

I. a step of mixing metal powder (M) and Si powder (Si) at a Si/M atomicratio ranging from 2.0 to 4.0 so as to form a mixed powder;

II. a step of filling the mixed power in a mold, and reducing carbon andoxygen contents by heating the entirety in high vacuum at acomparatively low temperature;

III. a step wherein the mixed power is heated in high vacuum and under alow pressure to execute synthesis and sintering of the metal silicide;and

IV. a step wherein the resultant material is further heated in anatmosphere of high vacuum or an inert gas and under a highpress-pressure, to a temperature just below the entectic point, so thatthe compactness of the material is promoted.

Preferably, the metal powder (M) used in this method is a high puritymetal powder having maximum grain diameter less than 10 μm, while the Sipowder. (Si) is a high purity Si powder having maximum grain diameterless than 30 μm.

Further, it is characterized that the mixed powder made of the metalpowder (M) and the Si power (Si) is subjected to areaction-melting-sintering process, so that silicide-synthesis,sintering and tightening of structure are carried out simultaneously.

Further, the aforementioned reaction-melting-melting-sintering processmay be executed by use of a hot-press method or a hot isostatic pressmethod.

The inventors of this invention have analyzed the reason of generatingparticles in the metal silicide target made of sintered alloy fromvarious point of view, and completed this invention based on theknowledge obtained by the analyzed results. More specifically, based onthe judgement that the particles generated heretofore in the refractorymetal silicide target produced by powder sintering method are induced asa result of abnormal electric discharge occurring in the pores (orvoids) produced in the target, and thereby collapsing the surroundingportions of these pores, various efforts have been exercised forimproving the density of the target and for reducing the number ofpores.

However, according to further study pursued by the inventors forclarifying the generating reason of the particles in the refractorymetal silicide target, various reasons such as collapse of eroded Siportion due to thermal stresses, collapse of the MSi₂ phase due to thedifference in sputtering rate between the MSi₂ phase and Si phase, andelse are found besides of the particles caused by the pores. To copewith the temperature rise caused by continuous bombard of high speedargon ions, the surface of the target is cooled from the rearside. Thusthermal stresses created by the thicknesswise temperature difference andthermal deformation of the target act on the surface of the target, andas a consequence, Si phase having a strength weaker than that of theMSi₂ phase is broken down to produce the particles. Particularly, theeroded surface of Si phase is much coaser than the rather flat surfaceof the MSi₂ phase, and the projecting portions of the Si phase tend tobe collapsed by thermal stress or deformation stress caused bysputtering cycles so as to easily produce particles. Further, Si phaseis eroded by sputtering in preference over MSi₂ phase, and when MSi₂phase is provided within continuously distributed Si phase, a force forseizing the MSi₂ phase is reduced according to the erosion of the Siphase, and MSi₂ phase is collapsed, in the form of single grains orcombined grains, thereby to produce particles.

The inventors of this invention find out that the generation of theparticles caused by the collapse of MSi=phase, which has been caused bythe erosion of Si phase owing to the thermal stresses or by thedifference in sputtering rate between the MSi₂ phase and Si phase, canbe substantially suppressed by a mixed construction of sputtering targetwherein the Si phase easily broken is made minute, and thus minuteformed Si phase is distributed discontinuously in the MSi₂ phase alsominute formed and coupled in an interlinked manner.

Furthermore, the inventors of this invention paid attention to carbonmixed in the target and liable to act as a particle generating source.More specifically, when the eroded surface of the target is observed ona magnified scale after the sputtering operation, it was found that theportion contaminated by carbon was not sputtered sufficiently, butremained in a projecting manner from the eroded surface, thus renderingplasma-discharge unstable so as to repeat abnormal discharge, andcausing generation of the particles.

The inventors also confirmed by experiments that the amount of carboncontained in the target widely affects the etching property of asilicide thin film formed by sputtering. More specifically, with carboncombined with Si component tends to produce SiC of highly insulativeproperty. The presence of SiC and mixing thereof into the thin filmtends to reduce the etching property of the thin film abruptly. Morespecifically, at a time when a circuit pattern is formed on a substrateapplied with a photoresist by means of a light exposing device, and thepattern is developed by a predetermined agent for obtaining a circuitpattern of an integrated circuit (IC) by etching the substrate formedwith a thin film, the ratio of remaining SiC as a residue increases, andthe provability of occurring defective circuit pattern and discontinuityof circuit increases.

In addition, the carbon deposits mixed in the silicide film in the formof particles have a light reflexibility different from other regions,and are easily exposed to light. As a consequence, regions having lightreflexibility locally different are formed on the surface of the film,and providing a uniform and high precision circuit pattern is therebymade difficult.

The inventors of this invention also paid attention to projectingportions created in the MSi₂ phase and Si phase as another source forgenerating particles. When the eroded surface of a metal silicide targetmanufactured by a conventional method is magnified and observed by ascanning type electron microscope (SEM), it is found that a great numberof minute projecting portions 3 are formed on the surface of coarse MSi₂phase grain and Si phase grain as shown in FIGS. 11A, 11B, and 12A, 12B,and that there is a close relation between the provision of theprojecting portions and the amount of the generated particles. Furtherstudy also reveals that the projecting portions are reduced inaccordance with the reduction of grain diameters of the MSi₂ phase andSi phase, and when the maximum grain diameter of MSi phase is selectedless than 10 μm, and the maximum grain diameter of Si phase is selectedless than 20 μm, generation of particles can be suppressedsubstantially.

As a result of further study for obtaining a sputtering target of highdensity and having a minute structure and least carbon contents,following facts are made apparent, and the invention is therebycompleted.

Where a mixed powder made of minute M powder and Si powder is placed ina mold and heated under high vacuum, and then subjected to a silicidereaction under a low press-pressure, and further thus obtained metalsilicide is sintered under a high press-pressure; carbon contained in Sisurface reacts with oxygen at a temperature lower than 1300° C.rendering Si evaporation to be significant, and carbon and oxygencontained in the resultant product are reduced in the form of CO or CO₂;

Oxygen contained in Si surface tends to react with Si to form SiO orSiO₂ gas, so that the oxygen contents are also reduced in this manner;

Metal (M) is entirely made into minute MSi₂ ;

A mixed structure wherein MSi₂ is coupled in a link form, and Si isdistributed discontinuously in the gaps of the link connections can bethereby obtained; and

Elimination of pores and tightness of the structure are promoted at atemperature just below the entectic point.

Inventors also find out that by providing an interface layer containingat least one kind of element selected from a group consisting of boron(B), phosphorus (P), antimony (Sb) and arsenic (As) between MSi₂ phaseand Si phase, coupling strength between these two phases is increased,and abrupt change in electric resistance can be avoided, thus realizingreduction of particle generation.

Herein, metals (M) such as molybdenum (Mo), tungsten (W), titanium (Ti),zirconium (Zr), hafnium (Hf), niobium (Nb), tantalum (Ta), vanadium (V),cobalt (Co), chromium (Cr), nickel (Ni) and the like capable of forminga metal silicide thin film of a comparatively small specific resistanceare used singly or in combination of two or more kinds for forming thetarget, and it is particularly advantageous to use refractory metalssuch as Mo, W, Ti, Zr, Hf, Nb and Ta for this purpose.

In comparison with the conventional electrode wiring materials, thesemetals exhibit lower specific resistance and higher corrosionresistivity at a high temperature. Thus when silicides of these metalsare used for electrode wiring of semiconductor devices, high-speedoperation of the semiconductor devices is made possible, and corrosiondue to various agents at the time of production, or oxidation at thetime of high temperature treatment can be substantially prevented.

By controlling three principal features, such as grain size of thematerial powder, heating temperature, and press-pressure, a mixedstructure of the sputtering target of this invention containing 400 to400×10⁴ MSi₂ phase grains per one mm² of the structure, and graindiameter thereof falling in a range of 0.5 to 30 μm can be obtained. Theaverage grain diameter of the MSi₂ phase becomes 2 to 15 μm, while theaverage gain diameter of the Si phase becomes 2 to 10 μm.

During the silicide synthesizing time, B, P, Sb, As contained in Simaterial as well as the elements such as Fe, Ni, Cr, Al and the like,and constituting unavoidable elements, are dispersed to be moved into aninterface region between the MSi₂ phase and the Si phase so as toproduce an interface layer that intensifys the conbining strengthbetween the two phases.

This invention has been completed based on the above describedknowledges.

The invention will now be described in more detail.

When a mixed powder of M and Si is heated under an appropriate pressure,the Si is softened while it is reacted with M to form MSi₂ of granularshape. Thus, at a portion where M is held in contact with Si, thetemperature is locally brought up by the reaction heat of MSi₂, so as tofurther soften Si. As a consequence, grains partly formed into MSi₂ arecoagulated around each MSi₂ grain, and thus coagulated MSi₂ grains arecoupled with each other so as to provide a link-coupled structure. Whenthe MSi₂ grains are separately distributed in Si phase, the Si phasehaving a larger sputter rate is eroded firstly in accordance with theprogress of sputter, so that MSi₂ phase tends to be dropped out easily.For this reason, it is preferable that MSi₂ phase grains are coupledtogether in an interlinked manner.

Further, when the grain diameter of MSi₂ phase exceeds 30 μm, projectingportions are formed during sputtering on the MSi₂ grain, thus creatingparticles. On the other hand, when the grain diameter of MSi phase isless than 0.5 μm, the MSi₂ phase easily drops out during sputtering tocreate particles. As a consequence, it is preferable that the graindiameter of MSi₂ phase is held in a range of from 0.5 to 30 μm, morepreferably in a range of from 2 to 20 μm.

In a case where the x value in a composition MSi_(x) is in a range offrom 2.0 to 4.0, and the grain diameter of MSi₂ is in a range of from0.5 to 30 μm, it is also preferable that MSi₂ of 400 to 400×10⁴ grainsare provided in each mm² of the mixed structure. In a case where thegrain diameter of MSi₂ is in the range of 2 to 20 μm, it is preferablethat MSi₂ of 2,000 to 300,000 grains are provided in each mm² of themixed structure.

Further, the size of MSi₂ depends on the grain diameter of the metalgrain forming the metal silicide. However, most of the M grains are in acoagulated state so that MSi₂ of different grain diameters are produced.According to increase of variation range of the grain diameter,projection and recess of the eroded surface due to sputtering becomesignificant, and because of the effect of the difference in surfacelevel, the generated amount of particles increases. For this reason, itis required to equalize the grain diameter as far as possible, and it isdesirous that average grain diameter of MSi₂ phase is in a range of from2 to 15 μm, preferably in a range of 5 to 10 μm.

Herein described average gain diameter is an average diameter of every100 grains of the metal silicide.

As for the shape of MSi₂ grains coupled in a linked manner, nearlyspherical configuration is most desirous. The reason of this resides inthat the spherical grain hardly drops out of the mixed structure formedwith the Si phase, and angular grain easily generates particles becauseof abnormal discharge. From this view-point, since metal grains obtainedby ion-exchange refining method are easily coagulated during a reductionprocess, and MSi₂ grains obtained by combining these M grains exhibitmuch projection and recess, it is required that the coagulation issuppressed by a treatment under a reduction condition hardly causingcoagulation, or by adding a dispersing agent at the time of mixingpowders. Otherwise, it is also preferable that the M gains produced by aChemical Vapor Deposition method, and hence having a good graindispersing property are used for obtaining MSi₂ phase.

The Chemical Vapor Deposition method (hereinafter termed CVD method) isa method wherein a material such as halide, sulfide, hydride and thelike is made into vapor phase at a high temperature, subjected to achemical reaction such as thermal decomposition, oxidation or reduction,and thus obtained reaction product is deposited on a substrate. Thismethod is widely used for producing semiconductors and insulation films.

On the other hand, Si reacts with M Grains to form MSi₂, with excessiveSi forcibly flowing around MSi₂ grains, so as to obtain a configurationhaving Si distributed discontinuously in the Gaps formed between MSi₂Grains combined in a link form.

Continuous distribution of Si invites collapse of Grains due to the factthat Si is eroded in preference to MSi₂ according to the progress ofsputtering, and because of reduction of mechanical strength owing to thethermal stresses created in the target during sputtering Si portionssusceptible to thermal shock tend to be broken down. For preventingGeneration of particles by improving mechanical strength, it isadvantageous that Si is distributed discontinuously in the Gaps of MSi₂.

Further, when the Grain diameter of Si exceeds 30 μm, ollapse of theeroded Si portion tends to occur due to the thermal effects. Inaddition, projecting portions formed in the Si phase during sputteringtends to generate particles, and therefore the maximum Grain diameter ofSi is selected less than 30 μm, preferably less than 20 μm.

When the deviation in Grain diameter of Si becomes large, the stressoccurs concentratedly in a part where grain diameter is large, so thatthe part is easily broken by repetition of the thermal stress. For thisreason, the average grain diameter of Si is selected preferably in arange of from 2 to 10 μm, and more preferably in a range of 3 to 8 μm.

Herein, grain diameter of Si is an average value between the maximummeasurement and the minimum measurement of Si phase provided in the gapsof MSi₂, while the average grain diameter of Si is an average value ofgrain diameters of 100 grains.

It is desirous that a raw material Si powder of high purity or of highpurity containing a doping agent is used for the production of thetarget. It is desirous to lower the content of the impurities containedin the high-purity Si powder as low as possible, because the impuritiesdeteriorate the characteristics of semiconductor element. For example, acontent of radio-active element such as U, Th causing a soft-error isrestricted less than 5 ppb. The content of alkaline metal element suchas Na, K causing movable-ion contamination is restricted less than 100ppb. Impurities mixed in the high-purity Si must be heavy metalelements, such as Fe, Ni, Cr and else, constituting deep-levelimpurities, are restricted less than 1 ppm, carbon causing particlegeneration and etching defect is restricted less than 300 ppm, andoxygen causing resistance increase is restricted less than 500 ppm.

The impurities such as carbon, oxygen, Na, K and else, contained in theSi powder have been adhered to the powder surface during Si crashingsteps, and reduction of these impurities can be attempted by subjectingthe impurity-contaminated Si powder to a heating process of from 1200°to 1300° C. under a vacuum lower than 10⁻⁴ Torr for 2 to 6 hours. It isdesirous that a material Si power thus heat processed is used for theproduction of the target.

Ordinarily, when a target is formed out of a material Si powdercontaining a doping agent, this doping agent tends to be dispersed andcondensed at the reaction and synthesis time to specific areas in theinterface of crystals. The doping agent thus dispersed causesdisturbance in crystal grating, and moves to boundries between the MSi₂phase and Si phase to form an interface layer.

By the existence of the interface layer, the bonding strength betweenthe MSi₂ phase and Si phase increases, and the MSi₂ phase is madedifficult to drop-out from the mixed structure of the MSi₂ phase and theSi phase. Further the existence of the interface layer of high dopingagent density in the boundary between the MSi₂ phase of low electricresistance and the Si phase of high electric resistance eliminatesabrupt variation of the resistance, so that abnormal discharge at thetime of sputtering is reduced, and generation of the particles caused bythe abnormal discharge can be suppressed.

As a result of further study for realizing smooth variation of electricresistance in the boundary between MSi₂ phase and Si phase, it is foundthat where a target is produced from Si powder and M powder, or fromMSi₂ powder, containing at least one kind of element selected from B, P,Sb and As, as a doping agent, and also containing an unavoidableelement, and electric resistance of the powders is controlled, thetarget thus produced exhibits an improved alignment in the electricresistance of the MSi₂ phase and the Si phase, and the sputtering speedtherefrom is also made uniform. Since an interface layer, in which theabove described element is diffused, is formed between the MSi₂ phaseand the Si phase, no abrupt variation of electric resistance occurs, anda target having an excellent interface strength is thereby obtained.

Among the above described doping agents, B, P, Sb and As are elementscapable of decreasing electric resistance widely, and when an Si phasecontaining these elements is used, electric resistances of both phasesare sufficiently aligned, rendering the sputtering speed to be uniform,and providing a thin film of stable composition and uniform thickness.At the time of sintering, these elements contained in Si phase arediffused to move into the interface region between the MSi₂ phase havingdisturbance or deformation of crystal grating and the Si phase so as toform an interface layer. At this time, elements such as Fe, Niunavoidably contained beside of B, P, Sb and As also impart similareffects.

As for the thickness of the interface layer, although it is different bythe amount of doping agent contained in the Si phase, a value in a rangeof from 100 to 10,000 Å is considered to be appropriate.

In a case where the thickness of the interface layer is larger than10,000 Å, the characteristics of the thin film tend to be varied, whilein a case where the thickness of the interface layer is less than 100 Å,the above described advantageous effects cannot be expectedsufficiently. More preferable range of the thickness is from 1,000 to8,000 Å.

The thickness of the interface layer can be detected by a highresolution secondary ion mass spectroscope (SIMS).

The SIMS executes sputter etching of a specimen by use of O²⁺ or firstorder ion of Cs⁺, and seizes the secondorder ions thereby generated foranalyzing impurities in the surface layer in a 3rd-order manner at ahigh sensitivity. The thickness of the interface layer is measured bymeasuring the profile in the depthwise direction of doping agentcontained in the Si phase until it reaches the MSi₂ phase.

Herein, the thickness of the interface layer is defined to be a distancefrom an inflection point located in an entailed portion of the profileof the doping agent in the Si phase to another inflection point.

The aforementioned electric resistivity of Si phase is preferablyselected in a range of from 0.01 to 100 Ω.cm. When the resistivity isselected less than 0.01 Ω.cm, the sputtering speed of Si phaseincreases, and thereby deeply eroded Si not only invites generation ofthe particles, but also makes it impossible to obtain a desired filmstructure. On the other hand, when the resistivity exceeds 100 Ω.cm, theabove described effects cannot be expected. More preferably, theresistivity of Si phase is selected in a range of from 0.1 to 10 Ω.cm.

On the other hand, portions contaminated by carbon are not sputteredsufficiently, but remain on the eroded surface in a projecting manner.As a result, plasma-discharge in these portions becomes unstable,repeating abnormal discharge in these portions, and inducing generationof particles. When a large amount of carbon is mixed in the thin film,etchaning tends to remain in the part at a time when wirings are formedin the part by etching, resulting disconnections due to faulty wiringand existence of insulating substances. For this reason, it is requiredthat the contents of carbon impurity is restricted less than 100 ppm,preferably less than 50 ppm, more preferably less than 30 ppm. Thecarbon contents is detected by a carbon detector by use ofcombustion-infrared ray absorbing method.

In a case where a large amount of oxygen impurity is contained in thetarget, the oxygen tends to be mixed in the thin film at the sputteringtime, and increases electric resistance of the thin film. For thisreason, the oxygen contents is suppressed preferably less than 150 ppm,more preferably less than 100 ppm. The oxygen contents is detected by anoxygen analyzer by use of an inert gas melting-infrared ray absorbingmethod.

The sputtering target of this invention is formed into a mixed structureof a minute granular MSi₂ phase and Si phase. This structure is obtainedsuch that a mixed powder formed out of M powder and Si powder issubjected to a sinter-synthesizing process so as to provide the MSi₂phase, and in this case, the mixing ratio of these powders is selectedto provide .a composition of MSi_(x) wherein x value is held in2.0<×<4.0. That is, excessive Si remains so as to stick around the MSi₂phase.

When the mixed powder of M and Si is heated under an appropriatepressure, Si is softened while it reacts with M to provide MSi₂. Atportions where Si grains are held in contact with M grains, thetemperature of the mixture locally rises up by the reaction heat so thatSi is further softened. As a result, Si grains are coagulated around thesurface of grains now being formed into MSi₂ composition so as topromote the combining reaction. On the other hand, MSi₂ phase and Siphase, or MSi₂ phase grains themselves are rigidly coupled together by adiffusion reaction, so that a large amount of not-yet reacted Si issomewhat softened and the excessive amount of Si is forcibly movedaround the MSi₂ -forming grains so as to tighten the structure.

The reason why the X value in the composition MSi_(x) is restricted to2.0<×<4.0 is as follows. In a case where the X value in the compositionMSi_(x) is made less than 2.0, a large tensile force is created in thesilicide film thus formed, thus deteriorating bonding nature between thefilm and the substrate and facilitating peeling-off from the substrate.Conversely, when the X value of the composition exceeds 4.0, the sheetresistance of thin film becomes high, thus making it improper to be usedas electrode wiring thin film.

Further, there is a relation between the density ratio of the target andgenerating amount of particles, and in a case of low density, plenty ofpores are provided in the target, abnormal discharge tending to occur inthe portions, and the part thereby collapsed causing generation of theparticles. For this reason, it is desirous that the density ratio of theentire portions of the target is held to be higher than 99%. Herein thedensity ratio (d=dt/ds) is a ratio between a theoretical density (ds)calculated from the component ratio of the sintered substance and thedensity (dr) of the sintered substance practically measured byArehimedes's method.

Further, the inventors of this invention found out that the separationof particles from the target during sputtering not only depends uponsurface defective layers created in the MSi₂ phase and Si phase, butalso is Caused by work defect layers, surface condition, or remainingstresses created at the time when the silicide sintered substance issubjected to machining such as grainding and finishing. That is, thegrainding and finishing of target have been heretofore carried out suchthat the work is scraped and ground by hard grains of a grinder rotatedat a high speed. In a ease where a rigid and brittle material such asthe silicide sintered substance consisting of a metal silicide andsilicon is worked by a method as described above, it is inevitable thatgranular chips are separated from the surface of the work. According tothe knowledge of the inventions, it is considered that the reasonresides in that at the time of grainding, minute cracks are created onthe surface of work by a stress caused by contact of the work with hardabrasive grains, and after the abrasive grains have passed, edgeportions of the cracks are pushed up by abrupt release of the stress,and separated in the form of fragment pieces. Ordinarily, at the time ofworking a brittle material, cutting depth or cutting load per eachabrasive grain is made suitably large, so that cracks are extended in alocal stress field formed by the grains, and by accumulating the minutecollapse of the material, the working of the material is progressed.Accordingly, on the worked surface of the silicide sintered substance, alarge number of work-defective layers such as grinding traces,dropped-out holes, and minute cracks are created.

When sputtering is executed by use of the target having these defectivelayers on the entire surface thereof, minute grains are stripped off anddropped out of the surface of the target by the impact of ions providedin plasma, with the above described defect portions taken as startingpoint, thus generating the particles. For this reason, it is desirous tofinish the surface of the target such that the surface roughness Ra(center line roughness) is maintained less than 0.05 μm, and the workdefective layers such as minute cracks and defective portions caused bythe machining are not remained substantially.

Herein, as is defined in Japan Industries Standard (JIS-B0601), when aportion of a roughness curve having a measured length l in the directionof the center line is extracted, the X axis is set to the center line ofthe extracted portion, the Y axis is set to the direction of thelongitudinal magnification, and the roughness curve is expressed byy=f(x), the surface roughness Ra defined in micrometer (μm) iscalculated as follows. ##EQU1##

To reduce the finished surface rougness and to substantially remove anyaftwork defective layers in which cracks and coming-off holes areformed, it is important to reduce the working unit relative to thedistribution of material defects. More specifically, it is necessary touse .abrasive grains having a smaller and uniform grain size or toreduce the load per abrasive grain by using a material such as a softpolisher improved in elasticity or viscoelasticity to limit the stresscaused in the material to a value lower than the breaking stress.

Accordingly, even in the case of a brittle material such as a sinteredsubstance including a metal silicide, when the afore-mentioned load isextremely small, the material exhibits only plastic deformation thusproviding no crack-forming region, so that it is made possible to obtainfinished surface having least amount of projection and recess andbright. As a practical method, lapping and polishing methods forfinishing the surface, and a mechano-chemical polishing method forfinishing the surface with extremely high precision are consideredpreferable.

The mechano-chemical polishing is a method wherein a conventionalmechanical method utilizing a Grinding stone, and a convevtionalchemical method utilizing chemical effects of eroding the polishedmaterial surface by a chemical agent, are used in combination.

However, practically it is difficult to finish a silicide sinteredsubstance-to a desired size by use of these methods only, and thereforeit is required that the surface is firstly worked by a more efficientmethod such as grinding, and then finished by the combined use oflapping and polishing steps.

In the above described surface working method, since the abrasive grainsize is reduced according to the order of lapping, polishing, andmechano-chemical polishing, roughness of the finished surface is alsominimized in this order. By applying such a working method to the metalsilicide target, the amount of particles generated from the target issubstantially reduced. According to the knowledge of the inventors thereis a corelation between the generated amount of the particles and theroughness of the surface. In order to suppress generation of particles,it is desired that the surface roughness Ra (center-line roughness) ofthe worked surface is less than 0.02 μm, preferably less than 0.05 μm.

In the sputtering caused by Ar ion irradiation, the ion impacting pointbecomes a high-stress field and is exposed to high temperature.Accordingly, when residual stress remains unevenly in the target surfacelayer portion, the stress is redistributed by the heat created duringsputtering, thus locally increasing the stress. As a result, largecracks including radial cracks are created, and the amount of theseparated particles is considerably increased. Accordingly, it ispreferable that the residual stress is reduced less than 15 kg/mm², morepreferably less than 5 kg/mm².

The manufacturing method of this invention will now be described in moredetail. The method comprises a step 1 where M powder and Si powder aremixed with each other at a predetermined ratio; a step II where themixed powder is heated at a low temperature for reducing the carbon andoxygen contents; a step III where the M/Si mixed powder is filled in amold, and subjected to a silicide reaction under a low hot-presspressure and a high vacuum, for executing synthesis of a refractorymetal silicide; and a step IV where the thus synthesized metal silicideis sintered under a high hot-press pressure so as to obtain a compactand tight structure. The temperature and press-pressure used in thesteps III and IV constitute very important factors for obtaining asintered substance of high density and compact structure.

The step I of the manufacturing method is a step for preparing andmixing M power and Si power so as to obtain a mixed composition at anSi/M atom ratio of 2.0 to 4.0. In this step of mixing M powder and Sipowder, the grain sizes of the two kind of powders impart significanteffect to the grain sizes of thus synthesized MSi₂ and Si interposed inthe MSi₂ grains. In order to provide the afore-mentioned minutestructure, it is preferable to use M powder of a maximum grain size lessthan 10 μm and Si powder of maximum grain size less than 30 μm.

The reason why the X value of the composition MSi_(x) is restricted to2.0<×<4.0 resides in that when the X value is less than 2.0, a largetensile stress is created in the thus formed silicide thin film, so thatthe bonding nature of the thin film to the substrate is deteriorated,thus tending to be peeled off from the substrate. On the other hand,when the X value exceeds 4.0, the sheet resistance of the thin filmbecomes high, and it becomes unsuitable to be used for providingelectrodes and wirings. According to this step, the raw material Mpowder and Si powder are mixed together at an Si/M atom ratio of from2.0 to 4.0 by use of a ball mill or a V-shape mixer of dry type so thata mixture of sufficiently uniform structure is thereby obtained. Unevenmixture is not advantageous because the composition and structure of theresultant target become uneven, and the property of a thin film therebyformed is deteriorated.

Herein, in order to prevent oxygen contamination, it is desirous thatthe mixing operation is carried out in vacuum or in an atmosphere ofinert gas.

Further, in consideration of a volatile loss of Si and SiO₂ from thesurface of the Si powder at a time when the powder is heated to a hightemperature, it is proper that an amount of the Si powder somewhatlarger than its objective value is mixed with the other powder. Theexcessive amount is selected less than 5% based on experience and inconsideration of the temperature, period and pressure and the like ofthe subsequent step.

In the step II, the mixed powder prepared by the step I, is heated at alow temperature and high vacuum so as to reduce carbon and oxygencontents. In this step, it is important that the heating temperature,holding time and the degree of vacuum are set to appropriate values in astate where no press-pressure is applied. More specifically it isdesirous to set the heating temperature in a range of from 1,000°to1,300° C. At a temperature lower than 1,000° C., removal of impuritiesis not sufficient, while at a temperature higher than 1,300° C.,silicide reaction starts, and the evaporation of impurities becomesinsufficient, thus providing a target containing large amount of carbonand oxygen. More preferably, the heating temperature is selected in arange of from 1,100° C. to 1,300° C.

It is advantageous that the holding time is set in a range of from 1 to10 hr in consideration of the heating temperature. When the holding timeis less than 1 hr, the above described advantage cannot be obtainedsufficiently, and when the holding time is longer than 10 hrs, theproductivity is reduced. On the other hand, in order to reduce carbonand oxygen sufficiently, the vacuum within the hot-press is preferablyset to a high vacuum less than 10⁻⁴ Torr, and more preferably less than10⁻⁵ Torr. However, when the degree of vacuum in the hot-press isabruptly increased, the mixed powder tends to flow-away out of the mold,so that the tightness of the sintered substance becomes insufficienteven after the execution of the subsequent step. Accordingly, it isdesirous that the degree of vacuum in the hot-press is increasedgradually until it becomes a value less than 100 Torr.

In the step III, degassed mixed powder is heated under a high vacuum andlow press-pressure to synthesize MSi₂ phase. In this silicide synthesisstep, it is required that the heating temperature and the press-pressureare set to appropriate conditions, silicide reaction is caused toprogress gradually, grow of MSi₂ grains is suppressed, and softened Siis caused to flow in gaps between MSi₂ grains. For this, it is desirousto set the heating temperature in a range from 1,000° to 1,300° C. In acase where heating temperature is less than 1,000° C., silicide reactionis not easily started, and in a case where it exceeds 1300° C., MSi₂grains grow by a rapid silicide reaction such that the grains becomecoarse and large. Accordingly, it is desirous that the heatingtemperature is set preferably in a range of from 1,100° C. to 1,300° C.

At this time, the heating speed is desired to be set to less than 20°C./minute for obtaining synthesized MSi₂ phase of a minute structure. Inorder to realize good controllability of the silicide reaction speed,and to prevent absorption of impurity gas, it is desired that thereaction is effectuated in an atmosphere of high vacuum less than 10⁻⁴Torr.

Further, since the press-pressure affects much upon the grain diameterof the MSi₂ grains, it is desirous to set the pressure in a range offrom 10 to 100 kg/cm¹. When the press-pressure is less than 10 kg/cm²,silicide reaction heat becomes low, and softening and flow of Si is notsufficient, thus entailing a defective structure of uneven Siseparation. On the other hand, when the press-pressure is larger than100 kg/cm², contacting pressure between M powder and Si powder becomeslarge, silicide reaction heat increases to accelerate reaction, and MSi₂grain size becomes large and coarse. The press-pressure is morepreferably set in a range of from 30 to 60 kg/cm².

As for the atmosphere at the time of silicide synthesis, a high vacuumless than 10⁻⁴ Torr is preferable as described before in considerationof the silicide reaction speed and absorption of impurity gas.

Step IV is a step wherein the sintered substance is heated in highvacuum or in an atmosphere of inert gas, under a high press-pressure,and at a temperature just below the entectic point so as to obtain aminute and compact structure of the sintered substance.

In this step of obtaining compactness of the sintered substance,press-pressure, heating temperature, and heating time at thistemperature are important for obtaining the compact structure.

The press-pressure used in this step is preferably held in a range of100 to 300 kg/cm² for promoting compactness of the sintered substance.When the press-pressure is lower than 100 kg/cm², the density of theresultant sintered substance becomes low containing a large number ofpores remained in the substance, while in the case where thepress-pressure exceeds 300 kg/cm², although the density of the sinteredsubstance becomes high, the mold made of graphite tends to be broken.Accordingly a range of from 150 to 250 kg/cm² is more preferablydesired.

As for the sintering temperature (heating temperature) T of this step, atemperature just below the eutectic point; that is, a range Ts-50≦T<Tsis preferable. Herein, eutectic temperatures Ts of W, Mo, Ti and Taconstituting the metal M are 1,400°, 1,410°, 1,330° and 1,385° C.,respectively. When T is lower than Ts-50, pores remain, so that it isdifficult to obtain a high density sintered substance. On the otherhand, when T is higher than Ts, Si phase melts to flow out of the mold,thus obtaining a sintered product having a large deviation in thecomponent ratio.

Further, the holding time of the heating temperature of the heatsintering is preferably selected in a range of from 1 to 8 hrs. When itis shorter than 1 hr, much pores remain, so that a sintered substance ofhigh density cannot be obtained, while when it is longer than 8 hrs, thedensity of sintered substance is not increased anymore so that theefficiency of manufacturing target is reduced. It is desirous that thedensifying sinter is executed in vacuum or in the atmosphere of inertgas for preventing contamination caused by mixing of impurities.Nitrogen atmosphere is not advantageous because it tends to produce Si₃N₄.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a scanning type electron microscope photograph of a metallicstructure of a target according to preferred embodiments of thisinvention;

FIG. 1B is a partial schematic drawing to be used for explaining themetallic structure shown in FIG. 1A;

FIG. 2A is a scanning type electron microscope photograph showing ametallic structure of a target according to reference and conventionalexamples;

FIG. 2B is a partial schematic drawing to be used for explaining themetallic structure shown in FIG. 2A;

FIG. 3A is a scanning type electron microscope photograph showing aneroded surface configuration of the target according to the preferredembodiments;

FIG. 3B is a partial schematic drawing to be used for explaining thesurface configuration shown in FIG. 3A;

FIG. 4A is a scanning type electron microscope photograph showing aneroded surface configuration of a target according to the reference andconventional examples;

FIG. 4B is a partial schematic drawing to be used for explaining thesurface configuration photograph of FIG. 4A;

FIG. 5A is a scanning type electron microscope photograph showing, inmuch enlarged manner, a projecting portion formed on the eroded surfaceof the target according to the reference and conventional examples;

FIG. 5B is a partial schematic drawing to be used for explaining theprojecting portion shown in FIG. 5A;

FIG. 6 is a scanning type electron microscope photograph showing theresults of element analysis of the surface of the projecting portionshown in FIG. 5A;

FIG. 7A is a metallic structure photograph of a target of theembodiments of this invention obtained by an optical microscope;

FIG. 7B is a partial schematic drawing to be used for explaining themetallic structure photograph of FIG. 7A;

FIG. 8A is a metallic structure photograph of a target according toreference examples obtained by an optical microscope;

FIG. 8B is a partial schematic drawing to be used for explaining themetallic structure photograph shown in FIG. 8A;

FIG. 9A is a metallic structure photograph of a target according toconventional examples obtained by an optical microscope;

FIG. 9B is a partial schematic drawing to be used for explaining themetallic structure photograph shown in FIG. 9A;

FIG. 10A is a scanning type electron microscope photograph showing aneroded surface of a target according to the embodiments of thisinvention;

FIG. 10B is a partial schematic drawing to be used for explaining theeroded surface photograph shown in FIG. 10A;

FIG. 11A is a scanning type electron microscope photograph of an erodedsurface of a target according to reference examples;

FIG. 11B is a partial schematic drawing to be used for explaining theeroded surface photograph shown in FIG. 11A;

FIG. 12A is a scanning type electron microscope photograph showing aneroded surface of a target according to conventional examples; and

FIG. 12B is a partial schematic drawing to be used for explaining theeroded surface photograph of FIG. 12A.

EMBODIMENTS OF THE INVENTION

The construction and effects of the present invention will now bedescribed in detail with respect to the following embodiments.

Embodiments 1 to 12

As shown in Table 1, a high purity metal powder made of W, Mo, Ta or Nband having a maximum grain diameter less than 10 μm was mixed with ahigh purity Si powder having a maximum grain diameter less than 30 μm ata Si/M atom ratio of 2.7, and the resultant mixed powder was furthersubjected to mixing treatment in a ball mill replaced with a high purityAr gas for 48 hrs. Thus treated mixed powder was filled in a mold,provided in a hot-press, and degassed in vacuum of 8×10⁻⁵ Torr, at atemperature of 1,200° C. for 3 hrs so as to reduce impurities of carbon,oxygen and the like.

Then silicide synthesizing and compactness providing sinter was executedunder a condition shown in Table 1, and this obtained sintered body wasthen ground and finished with electric discharge to obtain a target of adiameter 260 mm and a thickness 6 mm.

Reference examples 1 to 12

As a reference example, a high purity metal powder made of W, Mo, Ta orNb and having a maximum grain diameter less than 100 μm was mixed with ahigh purity Si powder having a maximum grain diameter less than 200 μmat a Si/M atom ratio of 2.7, and the resultant mixed powder was, withoutbeing heat-treated for degassing under a high vacuum, subjected to asilicide synthesizing and tightness-providing sintering process under acondition as shown in the Table 1. The resultant sintered body was thenmade into a target of a diameter 260 mm and a thickness 6 mm by grindingand discharge finishing the same.

Conventional examples 1 to 3

A mixed power was prepared by mixing a high purity metal powder made ofW, Mo, Ta or Nb and having a maximum grain diameter less than 100 μm,with a high purity Si powder having a maximum grain diameter less than200 μm at a Si/M atom ratio of 2.0. Thus prepared mixed powder was thenheated under a vacuum of 2×10⁻⁴ Torr and at a temperature of 1,300° C.for 4 hrs to obtain a semi-sintered substance, and thereafter it wasimpregnated with melted Si so as to provide a sintered substance of Si/Matom ratio 2.7. The sintered substance was then made into a target ofthe conventional EXAMPLE 1 having a diameter 260 mm and a thickness 6 mmby grinding and discharge finishing the same.

A mixed powder was prepared by mixing a high purity metal power made ofW having a maximum grain diameter less than 15 μm with a high purity Sipowder having a maximum grain diameter less than 20 μm at Si/M atomratio of 2.7. Thus prepared mixed powder was then heated under a vacuumof 8×10⁻⁵ Torr and at a temperature of 1,250° C. for 4 hrs to obtain asemi-sintered substance. The semi-sintered substance is then filled in apressure-tight sealed can, and then subjected to a hot isostaticpressing under a pressure of 1,000 atom to provide a sintered body. Thusobtained sintered body is ground, polished and discharge-finished toprovide a target of a diameter 260 mm and a thickness 6 mm constitutinga conventional example 2.

A mixed powder was prepared by mixing a high purity W powder having amaximum grain diameter less than 100 μm with a high purity Si powderhaving a maximum grain diameter less than 200 μm at Si/M atom ratio of2.5. Thus prepared mixed powder was then heated under a vacuum of 2×10⁻⁴Torr and at a temperature of 1,300° C. for 4 hrs to obtain asemi-sintered substance. The semi-sintered substance was then crashed,and added with silicide synthesized powder so as to obtain a Si/M atomratio of 2.7. The resultant substance was then subjected to hot-press inan Ar gas atmosphere under a condition of 1,380° C.×3 hrs to obtain asintered body. The sintered body was then grind polished and dischargefinished to obtain a conventional example 3 target having a diameter of60 mm and a thickness of 6 mm.

Microscope observation results of the structure of a sectional surfaceof the embodiment target and the reference example target are shown inFIGS. 1A and 1B and FIGS. 2A and 2B. As shown in FIGS. 2A and 2B, thestructure of the target according to the reference example exhibiteduneven separation of Si 2 and coarse MSi₂ 1, while the target of theembodiment shown in FIGS. 1A and 1B exhibited a minute and uniformstructure wherein MSi₂ 1 of maximum grain diameter less than 10 μm wasconnected in a link form, and Si 2 was distributed in the gaps of theMSi₂ 1 discontinuously. Further, as a result of analyzing the contentsof carbon and oxygen, it was found that in the target of the embodiment,the contents of carbon and oxygen were less than 50 ppm and 100 ppm,respectively, while in the target of the reference example, the contentsthereof were approximately 250 ppm and 1,500 ppm, respectively.

In the Table 1, there are also indicated the results of the case wherethe targets obtained in accordance with embodiments 1 to 12, referenceexamples 1 to 12 and conventional examples 1 to 3 were set in amagnetron sputtering apparatus, sputtering then executed under anargon-gas pressure of 2.3×10⁻³ Torr so that a silicide thin film ofapproximately 3,000 Å was formed on a five inch Si wafer, and a mixedamount of particles was then measured.

                                      TABLE 1                                     __________________________________________________________________________             Average                                                                             Silicide synthesizing                                                                       Sintering condition                                       grain condition     for tightening                                            diameter                                                                            Temperature ×                                                                         Temperature ×                                                                        Carbon                                                                            Oxygen                                                                             Density                                                                            Amount of                 M    MSi.sub.2                                                                        Si time     Pressure                                                                           time    Pressure                                                                           content                                                                           content                                                                            ratio                                                                              particles             No  powder                                                                             (μm)                                                                          (μm)                                                                          (°C. × hr)                                                                (kg/cm.sup.2)                                                                      (°C. × hr)                                                               (kg/cm.sup.2)                                                                      (ppm)                                                                             (ppm)                                                                              (%)  (No.)                 __________________________________________________________________________    Embodiments Examples                                                          1   W     7  8 1100 × 5                                                                          60  1400 × 5                                                                        250   25  34  99.4  14                   2   W     5  7 1150 × 4                                                                          50  1400 × 4                                                                        250   46  85  99.5  22                   3   W     5  5 1200 × 3                                                                          30  1390 × 4                                                                        250   87  145 99.8  35                   4   Mo    8  7 1100 × 5                                                                          60  1400 ×  5                                                                       250   21  27  99.3  13                   5   Mo    8  6 1150 × 4                                                                          40  1400 × 4                                                                        250   40  76  99.6  26                   6   Mo    6  6 1150 × 4                                                                          30  1390 × 4                                                                        250   90  124 99.7  38                   7   Ta    7  9 1150 × 4                                                                          65  1370 × 5                                                                        250   22  42  99.4  13                   8   Ta    7  8 1150 × 4                                                                          45  1360 × 4                                                                        250   34  92  99.6  24                   9   Ta    5  6 1200 × 3                                                                          35  1360 × 4                                                                        250   78  147 99.5  37                   10  Nb    8  7 1100 × 5                                                                          60  1370 × 5                                                                        250   26  28  99.4  21                   11  Nb    6  6 1150 × 4                                                                          40  1360 × 4                                                                        250   43  77  99.7  28                   12  Nb    6  6 1200 × 3                                                                          30  1360 × 4                                                                        250   88  132 99.6  39                   Reference Examples                                                            1   W    30 60 1350 × 4                                                                         150  1370 × 4                                                                        250  139 1320 96.5 234                   2   W    25 55 "        "    "       "    186 1470 97.3 321                   3   W    20 47 "        "    "       "    235 1580 98.2 373                   4   Mo   45 56 1350 × 4                                                                         200  "       "    127 1350 95.9 203                   5   Mo   33 50 "        "    "       "    190 1440 96.7 311                   6   Mo   23 45 "        "    "       "    236 1620 97.8 388                   7   Ta   55 55 1350 × 4                                                                         180  "       "    145 1390 96.8 248                   8   Ta   43 50 "        "    "       "    194 1470 97.7 331                   9   Ta   32 43 "        "    "       "    247 1680 98.4 386                   10  Nb   50 50 1350 × 4                                                                         250  "       "    147 1240 96.0 230                   11  Nb   46 42 "        "    "       "    188 1460 97.7 328                   12  Nb   30 40 "        "    "       "    246 1590 98.5 388                   Conventional Examples                                                         1   W    56 45 --            --            20  25  98.3 245                   2   W    12 22 --            --           147  180 99.3  84                   3   W    25 23 --            --           260 1560 98.7 340                   __________________________________________________________________________

As is apparent from FIG. 1, the amount of particles generated from atarget according to the embodiments of this invention was much smallerthan that according to the reference examples and the conventionalexamples. Further when the eroded surfaces of the targets formedaccording to the embodiments, reference examples and the conventionalexamples were observed by use of a scanning type electron microscope(SEM), numerous projections 3 were found out on the eroded surfaces ofthe targets obtained by the reference examples and the conventionalexamples as shown in FIGS. 4A and 4B. However, as shown in FIGS. 3A and3B, no projection was observed on the eroded surfaces of the targetsobtained by the embodiments of the invention.

A result of further magnified observation of a projection 3 having acomparatively large size found on the eroded surfaces of the targetsaccording to the conventional and reference examples is indicated inFIGS. 5A and 5B, and a result of subjecting the surface of theprojection 3 shown in FIG. 5A to an element-analysis by use of an X-raymicroanalyzer (XMA) is shown in FIG. 6. As is apparent from FIG. 6,carbon dispersed in white dot manner on the surface of projection wasobserved, and this carbon constituted a reason for separating particles.It was confirmed that a target according to either of the embodiments ofthe invention contributed much to improve yield of the production whenit was utilized to form electrode wiring of semiconductor devices.

Next, the property of the target will now be compared between a casewhere an interface layer is formed between the MSi₂ phase and the Siphase of the target (embodiments), and a case where no interface layeris formed (reference examples).

Embodiments 101 to 114

A high purity metal powder made of W, Mo, Ti, Ta, Zr, Hf, Nb, V, Co, Cror Ni, or a combination thereof and having an average grain diameter of2 μm was mixed with a high purity Si powder (containing B, P, Sb, As andother unavoidable elements such as Fe, Ni and else) having an averagegrain diameter of 20 μm, at an Si/M atom ratio of 2.6, and the resultantmixed powder was thereafter subjected to a dry mixing process for 72 hrsin a ball mill, inside of which was replaced by high purity argon gas.Thus processed mixed powder was then filled in a hot-press mold made ofhigh purity graphite. The entirety was then loaded in a vacuum hot-pressand degassed under a vacuum of 5×10⁻⁵ Torr and at a temperature of1,250° C. for 2 hrs.

Then, in a vacuum of 5×10⁻⁵ Torr and under application of 50 kg/cm²press-pressure, a metal silicide (MSi₂) was synthesized at 1,250° C.,.With high purity argon gas added as an internal atmosphere of thehot-press, and with the internal pressure raised to 600 Torr, thesynthesized MSi₂ was sintered at 1,370° C. for 2 hrs. The resultantsintered body was then ground and discharge-finished to obtain a targetof 260 mm diameter and 6 mm thickness.

Reference examples 101 to 114

For obtaining a target of examples 101 to 110, a metal powder of highpurity W, Mo, Ti, Ta, Zr, Hf, Nb, Co, Cr or Ni, having a 25 μm averagegrain diameter was mixed with a high purity Si powder of 40 μm averagegrain diameter at a Si/M atom ratio of 2.6, and then subjected tohot-press under following conditions:

hot-press temperature: 1,380° C.,

hot-press pressure: 250 kg/cm²,

internal atmospheric pressure of

1 8×10⁻⁵ Torr vacuum until 1,250° C.,

2 600 Torr argon gas in a range from 1,250° C. to 1,380° C.,

So that a target of a diameter 260 mm and a thickness 6 mm according toconventional method was obtained.

Further, for obtaining reference examples 111-114, a WSi₂, MoSi₂, TaSi₂or TiSi₂ powder having an average grain diameter of 80 μm was mixed witha high purity Si powder having an average grain diameter of 60 μm, at anSi/M atom ratio of 2.6, and then subjected to hot-press under conditionssimilar to those of the reference examples 101 to 110, so as to obtain atarget having a diameter 260 mm and a thickness 6 mm.

With respect to the targets obtained in the embodiments 101 to 114 andthe reference examples 101 to 114, average thickness of the interfacelayers, density ratios, and flexing-strength were measured, and theresults were indicated in Table 2. As is apparent from this Table, thetargets according to the embodiments 101 to 114 exhibit high density andhigh flexion-strength, and that MSi₂ phase and Si phase are combinedrigidly by the interface layer.

Further, sectional structures of the targets obtained by the embodiment,reference example and conventional example were observed by an opticalmicroscope, and the observed results are indicated in FIGS. 7A, 7B, 8A,8B and 9A, 9B, respectively. As is apparent from FIGS. 7A and 7B, in thecase of the present embodiment, a minute mixed structure of the MSi₂phase 1 and Si phase 2 having an average grain, diameter of 10 μm, wasobserved. In the case of the target according to the reference example,the Si phase 2 and the MSi₂ phase 1 were both coarse and large as shownin FIGS. 8A and 8B, and in the case of the target according to theconventional example, it was confirmed that the Si phase 2 and the MSi₂phase 1 were both coarse, as shown in FIGS. 9A and 9B, and formed into astructure easily generating the particles.

The results of that the targets obtained according to the embodiments110 to 114 and reference examples 101 to 114 were set in a magnetronsputtering apparatus, sputtering was executed under an argon gaspressure of 2.3×10⁻³ so as to deposite a silicide thin film of 3,000 Åthickness on a 5 inch Si wafer, and then the amount of the particlescontained in the thin film was measured, are also indicated in the Table2.

                                      TABLE 2                                     __________________________________________________________________________                                Target                                                        Average                                                                              Si powder                                                                              Average                     Produced                          grain      Electric                                                                           thickness                   thin film             M powder    diameter   resistance                                                                         of inter-                                                                            Density                                                                            Flexion                                                                             Carbon                                                                             Oxygen                                                                             Amount of             Example                                                                             or MSi.sub.2                                                                        MSi.sub.2                                                                        Si  Doping                                                                            ratio                                                                              face layer                                                                           ratio                                                                              strength                                                                            content                                                                            content                                                                            particles             No.   powder                                                                              (μm)                                                                          (μm)                                                                           agent                                                                             (μΩ · cm)                                                        (Å)                                                                              (%)  (kg/mm.sup.2)                                                                       (ppm)                                                                              (ppm)                                                                              (No.)                 __________________________________________________________________________    Embodiments                                                                   101   W      6  7  B   200   1760  99.6 52     22   65   14                   102   Mo     8  8  P    80   2200  99.8 50     28   73   12                   103   Ti     7  6  P   300   1640  99.5 48     30   80   17                   104   Ta     7  7  Sb  300   1550  99.7 46     27   77   19                   105   Zr     8   8 B    80   3200  99.6 44     33   66   8                    106   Hf     8  5  As   60   2720  99.5 42     20   72   11                   107   Nb     5  7  B   500   1420  99.4 48     30   67   18                   108   V      8  7  P   400   1670  99.5 45     23   57   14                   109   Co     7  8  P    50   3180  99.8 47     20   68   10                   110   Cr     7  6  Sb  100   2380  99.4 45     34   58   21                   111   Ni     6  7  B   200   1860  99.5 50     26   71   16                   112   Mo + W                                                                               8  6  P   800   1250  99.9 49     37   63   24                   113   Ta + Mo                                                                              8  8  P   100   2210  99.6 50     29   75   17                   114   Nb + Zr                                                                              8  8  Sb  500   1210  99.5 47     32   64   20                   Reference Examples                                                            101   W     33 38  --  2.3 ×  10.sup.10                                                              --    99.4 37    122  1270 146                   102   Mo    28 32  --  "     --    99.1 35    109  1180 157                   103   Ti    27 38  --  "     --    99.2 32    112  1230 150                   104   Ta    25 34  --  "     --    99.3 35    133  1260 166                   105   Zr    30 36  --  "     --    99.4 36    120  1130 147                   106   Hf    33 32  --  "     --    99.2 34    130  1290 167                   107   Nb    28 31  --  "     --    99.0 37    126  1210 177                   108   Co    32 30  --  "     --    99.1 31    143  1250 184                   109   Cr    27 39  --  "     --    99.0 33    137  1200 173                   110   Ni    29 32  --  "     --    99.2 35    140  1240 181                   111   WSi.sub.2                                                                           82 53  --  "     --    96.5 30    180  1480 535                   112   MoSi.sub.2                                                                          78 52  --  "     --    95.5 27    188  1570 505                   113   TaSi.sub.2                                                                          80 50  --  "     --    92.2 25    175  1530 622                   114   NbSi.sub.2                                                                          80 56  --  "     --    94.8 22    192  1450 536                   __________________________________________________________________________

As is apparent from the results shown in Table 2, the amount of theparticles generated from the target of the embodiments was extremelysmall.

The sputtering surfaces of the targets obtained by the embodiments,reference examples, and conventional examples were observed by ascanning type electron microscope (SEM), and the metal structures asshown in FIGS. 10A, 10B, 11A, 11B, and 12A, 12B were found out. Althougha large number of projections 3 were recognized on the sputteringsurface of the reference examples (FIGS. 11A, 11B) and the conventionalexamples (FIGS. 12A, 12B), no projection 3 was observed on the surfaceof the target according to the embodiments as shown in FIGS. 10A, 10B.It was confirmed from these results that a substantial improvement couldbe expected in the yield of production by using the target of thisinvention for forming electrodes and wirings of semiconductor devices.

Next, the effects imparted to the generation of particles from thedefective layer, surface condition and residual stress caused at a timewhen the sintered silicide substance is subjected to a mechanicalfinishing operation such as grinding for providing a target, will now bedescribed with respect to the following embodiments.

Embodiment 200

A sintered silicide substance (tungsten silicide) was cut by wireelectrical discharge machining into a diameter of 260 mm, and thereafterthe sintered substance was ground to have a thickness of 6 mm byemploying a vertical-axis rotary surface grinder with a grinding wheelSD270J55BW6 under conditions: grinding wheel peripheral speed of 1,200m/min; a table rotating speed of 12 rpm; and a grinding rate of 10μm/min.

After the rearside surface of the target was soldered to a backingplate, the front side surface thereof was worked with a lens polisherand 15 μm diamond abrasive grains for 60 hrs, and then with 3 μmabrasive grains for 10 hrs. An ultrasonic cleaner was used to remove theworking solution attached to the lapped surface, and the surface wasthereafter degreased by acetone and dried out.

As a result of observing the worked surface by a scanning type electronmicroscope (SEM), no grinding streaks or dropped-out holes caused bygrinding remained, and having no fine cracks caused by deformation.breaking action of the abrasive grains were recognized, thus assuringremoval of the work defect layers.

The roughness of the worked surface was observed with a surfaceroughness measuring apparatus (Talysurf), and the residual stress in theworked surface was measured with an X-ray stress measuring apparatus onthe basis of a parallel-inclination method. Table 3 shows the results ofthese measurements. The results of the corresponding measurements of aground surface, held as it is, are also shown as reference example 200in the Table 3.

After the target thus obtained was set in a magnetion sputteringapparatus, sputtering was executed by Ar ion irradiation, so that asilicide thin film of 3,000 Å was deposited on a 5 inch Si wafer. Theamount of particles contained in the thin film was measured.

The measured results are also indicated in Table 3. From the resultsshown in FIG. 3, it was confirmed that the amount of the particles wasremarkably reduced by the target according to the embodiment 200, andthat by the lapping operation, the amount of particles in the thin filmproduced by the target could be reduced widely.

Embodiment 201

A sintered silicide substance having a diameter of 260 mm was ground andlapped in the same manner as the embodiment 200, and was then polishedwith an acrylic resin polisher and 0.3 μm celium oxide abrasive grainsfor 10 hrs under conditions of polisher pressure of 1 kg/cm², andpolisher speed of 10 m/min. The working solution was removed byultrasonic cleaning, and the polished surface was thereafter degreasedby aceton and was dried, thereby finishing the target.

As a result of observation of the worked surface by an SEM, work defectlayers having grinding streaks, dropped-out holes and fine cracks causedby grinding were completely eliminated, and the surface was finished ina mirror-like state. The results of measurements of the surfaceroughness and the residual stress in the worked surface are also shownin Table 3. Irregularities in the worked surface were extremely small ascompared with the ground surface shown as reference example 200, andplastic or elastic deformations of the surface caused by grinding wereremoved almost entirely.

Magnetron sputtering was effected by use of this target to form asilicide thin film on a five inch wafer. The result of the measurementof the amount of particles mixed in the film is also shown in Table 3.As is apparent from the result, it was confirmed that the amount ofparticles separated from the target could be remarkably reduced by theimprovement in the surface property attained by polishing performed asfinal finishing.

Embodiment 202

A sintered silicide substance having a diameter of 260 mm was ground andlapped in the same manner as the embodiment 200, and was then polishedin a mechano-chemical polishing manner by use of a cloth polisher andSiO₂ powder of 0.02 μm for 20 hrs under a polisher pressure of 1 kg/cm²and polisher speed of 10 m/min. After ultrasonic cleaning, the polishedsurface was degreased by aceton and dried, thereby finishing a target.

As a result of SEM observation of the worked surface, no work-defectlayers caused by grinding were recognized, and the degree of smoothnesswas extremely high in comparison with the ground surface with respect tothe surface roughness and the residual stress, so that the workedsurface was equivalent to a non-distortion surface.

Magnetron sputtering was also effected by use of this target to form asilicide thin film on a 5 inch Si wafer, and the amount of particlesmixed in the thin film was measured. As a result, as shown in Table 3,substantially no particles were recognized, and it was confirmed thatthe work-defect layers and the residual stresses causing separation ofparticles could be completely removed by the final finishing.

                  TABLE 3                                                         ______________________________________                                                          Residual    Amount of                                                 Surface compressive generated                                                 roughness                                                                             stress      particles                                                 Ra (μm)                                                                            (kg/mm.sup.2)                                                                             (No.)                                           ______________________________________                                        Embodiment 200                                                                            0.010     2.4         18                                          Embodiment 201                                                                            0.007     1.5         12                                          Embodiment 202                                                                            0.002     0.5          5                                          Reference   0.82      12.3        250                                         example 200                                                                   ______________________________________                                    

Industrial Applicability

According to the sputtering target and the manufacturing method of thesputtering target, a target of high density and having high strength andminute structure, and therefore capable of substantially preventinggeneration of particles can be provided and therefor it is extremelyadvantageous for providing a thin film adapted to provide electrodes andwirings of semiconductor devices.

What is claimed is:
 1. A sputtering target comprisinga metal silicidephase comprising a metal silicide having stoichiometric composition ofMSi₂, where M is a metal, coupled in a link form and, an Si phasecomprising Si grains dispersed in the gaps of the metal silicide phasediscontinuously so as to provide a compact mixed structure, wherein acarbon content of the mixed structure is less than 100 ppm.
 2. Thesputtering target according to claim 1 wherein 400 to 400×10⁴ metalsilicide grains, each grain having a grain diameter in a range of from 5to 30 μm, are provided in a sectional area of 1 mm² of the mixedstructure, and wherein maximum grain diameter of said Si grains is lessthan 30 μm.
 3. The sputtering target according to claim 1 wherein anaverage diameter of said metal silicide grains is held in a range offrom 2 to 15 μm, and wherein an average diameter of the Si grains isheld in a range of from 2 to 10 μm.
 4. The sputtering target accordingto claim 1 wherein a density ratio of the target is more than 99%. 5.The sputtering target according to claim 1 wherein an oxygen content ofthe target is less than 150 ppm.
 6. The sputtering target according toclaim 1 wherein the metal forming the metal silicide is at least onemetal selected from a group consisting of tungsten, molybdenum,titanium, zirconium, hafnium, niobium, tantalm, vanadium, cobalt,chromium, and nickel.
 7. The sputtering target according to claim 1wherein an interface layer is formed between the metal silicide phaseand the Si phase.
 8. The sputtering target according to claim 7 whereina thickness of the interface layer formed between the metal silicidephase and the Si phase is in a range of from 100 to 10,000 Å.
 9. Thesputtering target according to claim 1 wherein said Si phase furthercomprises at least one member selected from the group consisting of B,P, Sb and As, and wherein an electric resistivity of the Si phase is ina range of from 0.01 to 100 Ω.cm.
 10. The sputtering target as claimedin claim 1, consisting of a metal silicide phase and an Si phase. 11.The sputtering target as claimed in claim 10, wherein said metal formingthe metal silicide is selected from the group consisting of W, Mo, Taand Nb.
 12. The sputtering target as claimed in claim 1, wherein themetal forming the metal silicide is at least one metal selected from thegroup consisting of W, Mo, Ta and Nb.
 13. The sputtering target asclaimed in claim 1, consisting essentially of a metal silicide phase andan Si phase.